Sunlight is a mixture of vertical and horizontal wavelengths of light. A polarized lens selects either wavelength of light, vertical or horizontal, to pass through, and blocks the other wavelength. Thus, the reflection or glare from water surfaces, concrete roads, metal object, etc., will be significantly reduced by a polarized filter. Without the polarization function sunglasses only reduce the total amount of light transmitted therethrough but do not function to filter vertical or horizontal wavelengths to reduce glare.
Conventional polarized plastic lens typically are manufactured by one of the following methods. In one method, flat polarized film typically made of polyvinyl alcohol (PVA) is packed with or without an adhesive with triacetate cellulose, or polycarbonate thin layer, cut to shapes and sizes and then formatted to given curves. Advantages of this process are that it is an easy process to perform and is relatively low cost. Weaknesses of this process are that it produces a relatively unstable optic curve, the lens is easy to scratch, no power correction lens is currently able to be produced, and the material is highly moisture absorptive which leads to the deterioration of anti-glare function in a short period.
In a second method, a so called “sandwich” method is used to laminate a formatted polarized film between two lenses. Advantages of this process are that it is able to produce power correction lens and a hard coating can be applied on the lens surface. However, because air can be introduced during the lamination process bubbling and foaming at the faces of the materials can result and the polarized lens is easily delaminates or separated during the lens edging process or lens wearing period.
In a third method a curved PVA films are incorporated directly in injection molding of acrylic or polycarbonate (thermoplastic polymers) or incorporated in the casting (polymerization) of thermosetting monomers. Advantages of this method are that it an easy process to perform and it can produce lenses with power and hard coating. Weaknesses of this method are that the cost needed for manufacturing set up is relatively high and yield is relatively low, mainly due to material stress, uneven color density and distortion of PVA film inside the lens.
The abovementioned direct molding method and casting method often make the inserted polarized film in an unstable position in the molds and as a result reflect a wave from optic vision; consequently, these methods can generate an unwanted prism power and poor optic function.
The conventional plastic polarized lenses currently marketed have less than optimal resistance to heat and moisture, which leads often to deterioration of anti-glare function after a short period of wearing. This occurs because the polarized film may not be protected and/or isolated by suitable plastic materials completely. Moreover, the conventional plastic polarized lens, compared to those made of the mineral glass, has lower abrasion hardness and resistance. In addition, both conventional plastic and mineral glass polarized lens have poor impact resistance. The polarized lens is very suitable to wear outdoor activities and sport purpose; however, there are few lenses which offer superior impact-resistance function.
It would be desirable to have a method of forming a polarized lens that not only can use polycarbonate materials (by bonding two completely different resin materials between thermoplastic and thermosetting), but also can offer scratch resistance and superior impact resistance.
Conventional polycarbonate (thermoplastic polymer) or plastic (thermosetting monomer) photochromic lenses are made by either inclusion of an organic photochromic dye throughout the resin material or by the Trans-Bonding™ or imbibition (i.e., the absorption of a liquid by a solid or gel) method, where photochromic dye is driven into the front surface of the lens. The amount of light transmittance through the lens will be activated through the UV (ultraviolet) light exposure. The higher the UV light exposure the lower the amount of light transmittance to shade the light (activation of photochromic dyes), and vice versa.
Bonding thermoplastic materials, such as polycarbonates used in lenses as the power portion, to thermosetting materials, such as photochromic monomers is challenging, if it is done outside of the molding process. Molding methods are done at temperatures so high as to typically destroy or diminish the activation function of the photochromic dye inclusion in the polycarbonate resin. One photochromic polycarbonate lens currently commercially available made by the Trans-Bonding™ method is available as Transition™ lenses polycarbonate from Transitions Optical, Inc., SOLA International, Essilor, Younger Optics, and the like.
It would be desirable to produce a photochromic lens in a thermosetting material which can be built on a polycarbonate lens while retaining optical photochromic activity. It would be desirable to have a method of using the photochromic monomer to build upon a polycarbonate lens to manufacture a high optic quality of significantly less inner stress fused polycarbonate photochromic lens as well as fused polycarbonate photochromic polarized lens. It would also be desirable to have a method that would similarly produce a polarized polycarbonate ophthalmic lens.